#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

#define NUM_THREADS 10

typedef struct pair
{
    int x;
    int y;
    pthread_mutex_t lock;
} pair;

void pair_init( pair *p )
{
    p->x = 5;
    p->y = 995;
    pthread_mutex_init( &p->lock, NULL );
}

void pair_swap( pair *p )
{
    int tmp;

    pthread_mutex_lock( &p->lock );
    tmp = p->x;
    p->x = p->y;
    p->y = tmp;
    pthread_mutex_unlock( &p->lock );
}

int pair_sum( pair *p )
{
    int sum;

    pthread_mutex_lock( &p->lock );
    sum = p->x + p->y;
    pthread_mutex_unlock( &p->lock );

    return sum;
}

void *run( void * param )
{
    pair *p = (pair *) param;
    int i;

    for( i = 0; i < 100000; i++ )
    {
        pair_swap( p );
        if( pair_sum( p ) != 1000 )
        {
            printf( "OOPS!!!\n" );
            return NULL;
        }
    }

   return NULL;
}


int main( )
{
    pthread_t tarray[ NUM_THREADS ];
    pair thePair;
    int i;

    pair_init( &thePair );

    for( i = 0; i < NUM_THREADS; i++ )
        pthread_create( &tarray[ i ], NULL, run, (void *) &thePair );

    for( i = 0; i < NUM_THREADS; i++ )
        pthread_join( tarray[ i ], NULL );
    
    pthread_exit( NULL );
}